The present invention, generally, relates to storage systems, more particularly, to migration of data to a sequential access medium in a storage system.
A linear tape file system (LTFS) is software that allows for the performance of standard file operations to a tape medium through a file system interface. Technical development of LTFS format specification is now continued in SNIA (Storage Networking Industry Association) TWG (Technical Work Group). Several implementations of LTFS have been developed for tape drives and tape libraries. Hierarchical storage systems integrating a primary storage tier with LTFS as a secondary storage tier have been also developed, in which part of files in the primary storage tier is stored on tape media in the LTFS format.
Since the tape medium does not allow random access due to its sequential nature, newly created data is always appended to the tape medium. Data deletions just erase pointers to the data. Data updates always append updated data to the tape medium and just modify the pointers so as to point the updated data. So, space on the tape medium that is occupied by deleted or updated obsolete data may suppress capacity of the tape medium. In the hierarchical storage systems, there is provided a process referred as a “migration”, in which files are moved from the primary storage tier to the tape media in the secondary storage tier. The migration process can be scheduled at specific time, for example, off-peak hours. However, such migration process may deteriorate utilization of the tape medium due to the obsolete data on the tape medium.